| Title | A Novel View of Cement Failure with Application to Geothermal Well Construction |
|---|---|
| Authors | Catalin TEODORIU, Mi Chin YI, Adonis ICHIM, Saeed SALEHI |
| Year | 2018 |
| Conference | Stanford Geothermal Workshop |
| Keywords | well construction, well cement, shear failure, crush, well integrity |
| Abstract | Geothermal wells are designed following oil and gas practice but have a longer expected life span, and thus their integrity evaluation is based on the same standards and requirements of hydrocarbon wells. Thermal cement degradation is known to occur at temperatures higher than 110°C and many researchers have focused their efforts to develop new recipes that will withstand the high temperatures encountered in these wells. Although other scholars have focused on cement compression and tension strength and its evolution with time and temperature, a closer look at geothermal wells will show that the major load on the cement is generated by the inevitable casing expansion and its effects at the cement-casing contact. Several works have related geothermal well failures to the casing-cement debonding process. However, field data have shown that the casing movement does not correlate with the debonding theory. The major assumption is that the cementing hardware such as centralizers or collars do not restrict casing movement. If in some situations this might be the case, the casing couplings behavior could be the answer to improve the understanding of geothermal wellbore failure. This paper proposes a cement strength investigation setup, aimed at identifying the cement strength under a special shear load, simulating the coupling-cement interaction. Although cements are tested for shear through standardized bending tests, such test is not truly relevant for the annular cement, and as a result a new procedure to test this load on well cements is necessary and defined in this paper. The new method replicates the interaction between the casing couplings and cement, and results will help engineers improve their well design and increase the well integrity for the life of the geothermal well. |